Conventionally, there is a known technique that stabilizes the behavior of a vehicle such as an automobile during turning. For example, this technique sets the control amount corresponding to the deviation between a standard turning state quantity (a standard yaw rate) and an actual turning state quantity (an actual yaw rate), so as to perform a turning control. The standard turning state quantity (the standard yaw rate) is calculated based on a stability factor, a time constant coefficient of steering response, and similar parameter value that are parameter values related to turning characteristics. The stability factor, the time constant coefficient of steering response, and similar parameter value are changed depending on conditions such as the number of occupants and the superimposed load of the vehicle during running. For example, Patent Literatures 1 and 2 disclose techniques for estimating these parameter values based on an actual yaw rate, a lateral acceleration, a vehicle speed, and similar parameter during running.